Grain-oriented electrical steel sheet and method for manufacturing the same

Abstract

An excellent low noise property and excellent low iron loss property are obtained. A grain-oriented electrical steel sheet includes refined magnetic domains formed by electron beam irradiation. When the maximum magnetic flux density is 1.7 T, the grain-oriented electrical steel sheet has a residual magnetic flux density of 0.1 to 0.7 times the residual magnetic flux density before the electron beam irradiation and a maximum magnetizing force of 1.1 to 2.0 times the maximum magnetizing force before the electron beam irradiation.

The invention claimed is: 
     
       1. A grain-oriented electrical steel sheet comprising refined magnetic domains,
 wherein, in a condition excited by a magnetic field having a maximum magnetic flux density of 1.7 T, the grain-oriented electrical steel sheet has:
 (i) a residual magnetic flux density that is 0.1 to 0.7 times the residual magnetic flux density measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours, and 
 (ii) a maximum magnetizing force that is 1.1 to 2.0 times the maximum magnetizing force measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours. 
 
 
     
     
       2. The grain-oriented electrical steel sheet comprising refined magnetic domains according to  claim 1 , wherein the grain-oriented electrical steel sheet has a hysteresis loss at 50 Hz and 1.7 T of 0.28 W/kg or less. 
     
     
       3. The grain-oriented electrical steel sheet comprising refined magnetic domains according to  claim 1 , wherein the grain-oriented electrical steel sheet has:
 (i) a residual magnetic flux density that is 0.1 to 0.5 times the residual magnetic flux density measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours, and 
 (ii) a maximum magnetizing force that is 1.1 to 1.5 times the maximum magnetizing force measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours. 
 
     
     
       4. The grain-oriented electrical steel sheet comprising refined magnetic domains according to  claim 2 , wherein the grain-oriented electrical steel sheet has:
 (i) a residual magnetic flux density that is 0.1 to 0.5 times the residual magnetic flux density measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours, and 
 (ii) a maximum magnetizing force that is 1.1 to 1.5 times the maximum magnetizing force measured after the grain-oriented electrical steel sheet is subjected to annealing in a nitrogen atmosphere at 800° C. for 3 hours. 
 
     
     
       5. A method for manufacturing the grain-oriented electrical steel sheet of  claim 1 , the method comprising:
 subjecting a steel slab to hot rolling to obtain a hot rolled steel sheet; 
 subjecting the hot rolled steel sheet to hot band annealing to obtain a hot rolled steel sheet after hot band annealing; 
 subjecting the hot rolled steel sheet after hot band annealing to cold rolling once or cold rolling twice or more with intermediate annealing in between to obtain a cold rolled steel sheet with a final sheet thickness; 
 subjecting the cold rolled steel sheet to decarburization annealing to obtain a cold rolled steel sheet after decarburization annealing; 
 applying an annealing separator including MgO to a surface of the cold rolled steel sheet after decarburization annealing and then subjecting the cold rolled steel sheet after decarburization annealing to final annealing to obtain a steel sheet after final annealing; and 
 subjecting the steel sheet after final annealing to magnetic domain refining treatment with electron beam irradiation; 
 wherein during the magnetic domain refining treatment, the electron beam irradiation is performed with a beam diameter of 220 μm or less in an orthogonal direction that is orthogonal to a scanning direction of the electron beam, and with a ratio of beam maximum intensity in the orthogonal direction with respect to beam maximum intensity in the scanning direction of 0.7 or more to 1.3 or less; and 
 wherein the electron beam irradiation is performed using two or more beam control coils, an accelerating voltage of 90 kV or more, and a stigmator, 
 thereby producing the grain-oriented electrical steel sheet of  claim 1 .